Method for the froth flotation of slimed minerals and ores



United States Patent 3,151,962 METHQD FGR THE FRQTH FLQTATEON 0FSLllvliED MENERALS AND GEES James B. Duke, Menlo Park Terrace, Metuchen,N.J., assiguor to idinerals dz Chemicals Phiiipp Corporation,

Menlo Park, Ni, a corporation of Maryland Filed Feb. 1, 1961, Ser. No.86,502 it tllairns. (Ci. 209-3} The subject invention relates generallyto improvements in the froth flotation of finely divided or slimedmulticomponent mineral masses and ores. In essence, the subjectinvention constitutes an improvement over the froth flotation proceduredescribed in a copending US. patent application, Serial No. 779,061, nowPatent No. 2,990,958, filed December 9, 1958, of which I am acoinventor.

In accordance with the process of said copending application, thebeneficiation of very finely divided (slimed) multicomponent mineralmasses and ores by froth flotation is facilitated by conditioning anaqueous pulp of such slimed minerals or ores with a collector reagentselective to one component of such mineral or ore, leaving residualcomponents water wettable, and with collectorcoated, finely dividedparticles of an auxiliary mineral which are floatable in the reagentizedpulp. The latter report in the froth product in intimate associationwith the oiled component of the feed and, in so doing, they enhance orpromote the flotation of the oiled components of the feed which arenormally not amenable to efficient selective flotation. The machinedischarge product is a concentrate of the water-wettable components ofthe feed. It is postulated that the oiled auxiliary mineral particlesform a nucleus for the attachment of the finely divided oiled fractionof the feed and that the loaded auxiliary particles thus formed arebetter adapted to air-bubble attachment than the selectively oiled feedparticles. Thus, in effect, the oiled auxiliary nflnerals carry theslimed selectively oiled feed into the froth. For this reason, the oiledauxiliary particles are referred to hereafter as the oiled carrier.

By application of the novel conditioning treatment, described above,slimed minerals and ores, never heretofore concentratable by frothflotation, may now be beneficiated with an excellent degree ofefficiency. The method thus comprises a novel concept in the flotationart that extends its application to slimed minerals in the minus 10,minus 5, and minus 2 micron particle size ranges.

In carrying out this process, the carrier particles are preferablyintroduced into the feed pulp and the admixed pulp conditioned.Alternatively, the feed pulp and the pulp of the carrier mineral may beconditioned separately and the reagentized pulps admixed. A wide varietyof oiled carrier particles are useful in the process since apparentlythe oiled carrier particles function by a physical mechanism to improveflotation rather than by a chemical mechanism. The carrier mineralparticles are prefer ably largely minus 325 mesh, with extremely finematerials, microns or finer being eminently suitable. The carrier isemployed in amount by Weight at least equal to that portion of the feedwhich is to be floated and usually in appreciably greater quantity.

One of the characteristics of the process is that the froth product,obtained by aerating a pulp conditioned in the novel manner describedabove, generally tends to be extremely voluminous and persistent. Thefroths are Wet to the touch in spite of the fact that they are amplymineralized, indicating that the foams have poor drainage properties. Inthe latter respect, the froths differ fundamentally in nature from themineral-poor, voluminous froths sometimes developed because of the useof excessive frothing agents in conventional flotation processes.

As a result of the poor drainage of the foams, waterwettable feed slimesin the aqueous pulp tend to become entrained in the froth product. Thishas the obvious eflect of impairing product recovery in case thevaluable mineral reports in the machine discharge product. In case thevaluable mineral reports in the froth product, product grade isadversely affected. While these eifects of poor foam drainage are easilycoped with in batch laboratory scale flotation tests by allowingsufficient time for the pulp to drain from the foam before refloatingthe pulp and by proper manipulation of the foam, in continuous flotationcircuits the metallurgy of the process is adversely affected.

Thus, for example, in the flotation of colored impurities fromdiscolored kaolin clay. (a naturally slimed mineral) with negative-ionreagents selective to the colored impurities and with oil carrierparticles, such as oiled calcite or oiled sulfur, there results a veryWet, voluminous froth containing entrained clay. While the froth productfrom the initial flotation can be refioated sev-. eral times, asdescribed in said copending application, and the machine dischargeproducts from each of these flotations combined to provide a highbrightness kaolin clay product containing a small percentage of TiO andother coloring purities, in practice the clay recovery obtainable incontinuous operation has not matched results obtained in laboratoryscale batch flotation. Thus, a typical weight recovery in the firstflotation in continuous plant scale runs operating on the process withdiscolored clay is about 50% to 60%, and the overall weight recoveryobtained by refloating the initial froth product three times andcombining the four machine discharge products is typically to based onthe dry weight of the original kaolin clay. In contrast, in batchoperations utilizing the same feed and conditioning reagents, recovcryof the order of to is realized. Such results indicate that the recoveryproblem is a physical one, tied in with the poor drainagecharacteristics of the froth product, rather than one of inadequateselectivity of reagents. Variations in recovery are experienced withclay feeds of different origin.

In addition to its adverse effect on the metallurgy of the process,other obstacles are associated with the V0- luminous nature of the frothin commercial operation of the carrier flotation process. One of thedifliculties is that the flotation machines mustbe equipped withspecially large launders which are able to handle the voluminous froths.Further, special discard drains must be equipped to dispose of thepersistent froth product when it is not treated for recovery of mineralvalues therein.

Accordingly, a principal object of my invention is the provision of amethod for improving upon the properties of the foam produced bysubjecting to froth flotation a pulp of a slimed ore (or multicomponentmineral mass) which has been conditioned with a collector reagentselective to one component of said ore (or multicornponent mineral mass)and with collector-coated carrier particles.

A more particular object of this invention is to improve upon thedrainage properties of the foam, so as to eflect an improvement in themetallurgy of the carrier flotation process described above.

Still another object of this invention is to reduce the volume of foampresent in the froth product so as to obviate the need for special plantequipment to handle such froth.

Yet another important object is to utilize the improved physical natureof the froth product to improve further the metallurgy of the carrierflotation of slimed multicornponent minerals and ores in a continuousoperation in which the froth product is refloated.

A more particular object is to discard an initial portion of therefloated froth product before the second float subjected to an initialfroth flotation.

is subjected to further reflotation, whereby only a residual portion ofthe refloated product is subjected to further reflotation, therebyimproving the overall recovery of the composited machine dischargeproducts.

A further more specific object is to'improve upon the recovery ofbeneficiated clay machine discharge product without sacrifice in productgrade in a continuous commercial process in which the froth product isrefloated for recovery of'clay values therein.

Still another object of the invention is the provision of an improvementin the method for carrying out a process for the continuous carrierfroth flotation of discolored kaolin clay which calls for no additionalplant equipment. 7 7

Further objects and advantages will be readily apparent from thedescription of my invention taken in connection with the accompanyingdrawing which shows a flowsheet of a typical plant practicing the methodon a discolored kaolin clay feed.

The present invention is a result of my discovery that a hydrocarbon oilmay be utilized in a novel manner, hereinafter described, to effect aremarkable improvement in the physical nature of the froth productobtained by aerating a slimed feed pulp conditioned with solid carrierparticles in accordance with the method of US. Patent No. 2,990,958. Oneform of this invention is a result of my surprising discovery that whenthis hydrocarbon oil treatment is used, the initial froth product obtained by refloating the froth product is of a considerably higher gradethan is the froth subsequently developed. Tris phenomenon is utilized toeffect an improvement in recovery of the machine discharge product or animprovement in concentrate grade.

Briefly stated, in accordance with the present invention the desiredimprovement in the physical properties of the froth product obtained bythe flotation of a dispersed conditioned pulp of slimed multicomponentmineral mass and carrier mineral particles is obtained by furtherconditioning such a pulp with inert hydrocarbon oil before the admixedpulp of feed and oiled carrier particles is This is preferably done byforming a dispersed admixed pulp of feed and carrier mineral particles,conditioning the admixed pulp for flotation with a collector reagentselective to a component of the feed and also selective to the carriermineral particles, then postconditioning the pulp with my hydrocarbonoil and subjecting the thus conditioned pulp to froth flotation. Thefroth product obtained by aerating the conditioned pulp which has beentreated with my hydrocarbon oil is relatively dry, providing gooddrainage for the pulp, rather than wet and conducive to the entrainmentof slimed water-wettable matter in the feed as it would be in theabsence of the hydrocarbon oil treatment.

Thus, for example, in the beneficiation of discolored kaolin clay bycarrier flotation in a continuous process in which the froth isrefioated a plurality of times, the total quantity of beneficiated clayreporting in the underflow is greater, without sacrifice in clay grade,than when the postconditioning hydrocarbon oil treatment is omitted, allother factors being equal. With certain hydrocarbon oils an improvementin clay brightness is also realized.

Further, the froth volume is reduced appreciably as a result of thehydrocarbon oil treatment so that the froth may be handled in the usuallaunders or plant drains, thereby avoiding the requirement forspecialized plant equipment.

From the above, it is apparent that my use of a hydrocarbon oil with acollector-coated slimed feed to improve upon the physical properties ofthe froth product is different from the prior art use of similar oilswith conventional (i.e., deslimed) flotation feed as a replacement for apart of the ionic collector reagent for the purpose of reducing reagentcosts or to improve upon the selectivity of the collector. My oil isincorporated into a pulp in which mineral particles have already beencollector coated and, while in some instances an improvement incollection may be realized, such result is incidental to the principalbenefit of foam control in the froth product.

In accordance with an embodiment of this invention, the initial frothproduct obtained with the hydrocarbon oil postconditioning treatment issubjected to continuous reflotation in a second machine containing aplurality of cells in series. The float product from the initial cellsof the second machine is separated and only the float products from theother cells of this machine are refloated in a separate machine. In manyinstances, the refloated material is handled in the third machine in thesame manner that it was treated in the second machine. This may berepeated in subsequent machines until the final machine in which thefroth is handled as a whole. The machine discharge products of thevarious machines are combined when valuable minerals are containedtherein. When valuable minerals are in the froth products, all of theseare combined, including those separated out in the intermediatereflotation machines. By handling the froth products in this manner,optimum yield of machine discharge product is obtaincd without sacrificein grade and without the requirement for additional equipment.

' To obtain such a result with carrier flotation by separating aninitial froth product, it is essential that the process operate on aslimed feed pulp which has been conditioned, as described above, with myhydrocarbon oil since the method depends upon the excellent drainage ofthe foam obtained with the oil post-treatment, especially theexceptional drainage properties of the initial part of the frothsobtained by reflotation of froth of a previous flotation step.

Even a cursory review of this procedure for handling the froth productindicates that it involves a departure fromthe usual procedure for frothflotation of minerals and ores which, in general, treat the concentratesor underflows from individual flotation machines as a unit, eithertreating, recycling or discarding such products as a whole.

This invention will be described in detail with especial reference toits application to the beneficiation of dis colored kaolin clay. It willbe distinctly understood that my novel hydrocarbon oil conditioningtreatment is applicable to improving the nature of the froth obtained byaerating other slimed pulps conditioned with other oiled carrierparticles in accordance with US. Patent No. 2,990,958. It follows thatthe improved quality of froth obtained in this manner may be utilized,in adapting the process to continuous flotation with reflotation of thefroth product, to effect an improvement in yield of machine dischargeproduct or improvement in concentrate grade with feeds other than clay.

Initially, raw clay is dispersed in water, preferably using sodiumsilicate as the dispersant for the clay. The clay must be in a dispersedstate in the subsequent conditioning treatment since clay in aflocculated condition is not amenable to proper conditioning. The claymay be Whole clay or a fine fraction thereof.

Before oiling the clay pulp, I prefer to add my carrier particles, usingsuch'particles in an amount of 5% to 200%, based on the weight of clayfeed. As examples of suitable particulate auxiliary minerals, which,when collector coated, are used in conditioning the clay feed, may bementioned calcite, sulfur, barytes, kyanite, silica sand, marble,magnetite and fluorspar admixtures. Suitable reagents for floating theauxiliary minerals above specified are described in Taggarts Handbook ofMineral Dressing, Section 12, pp. 116-120 (1950 edition), 'or may beexperimentally determined' However, it will be readily apparent to thoseskilled in the froth flotation art that any mineral which may beappropriately conditioned for flotation in the presence of thereagentized kaolin pulp is within the compass of my invention. Theparticle size of the particulate auxiliary material may vary within arelatively wide range, which, of course, must lie within the range ofparticles floatable in the presence of the reagentized clay. Generallyspeaking, particles somewhat finer than 325 mesh may be preferred toparticles coarser than 325 mesh.

The admixed pulp, preferably at a 20% to 30% solids level, is thenconditioned with a negative-ion collector reagent capable of selectivelyoiling the colored impurities in the clay concurrently with oiling ofthe carrier particles by coating these particles with an orientedhydrophobic film. Higher fatty acids such as oleic acid are particularlysuitable collectors. Other fatty acid collectors include tall oil fattyacids, resin acids, sulfonates of these and like acids, such assulfo-oleic acid, and soaps of the aforementioned acids. The negativeion reagent may comprise one or more of the above collectors. Inaddition to the negative-ion collector, I incorporate an alkalinematerial, preferably ammonium hydroxide, since I realize optimumconcentration in a circuit having a pH between 8 and it). Also,preferably I incorporate a mat rial selected from the group consistingof ammonium sulfate, magnesium sulfate and potassium sulfate.Preferably, the fatty acid is used in the form of an emulsified mixturewith a mahogany sulfonate. The latter is an oil-soluble petroleumsulfonate prepared by sulfonating, usually with concentrated or fumingsulfuric acid, certain petroleum fractions. Mahogany sulfonates arecommercially available in the form of sodium, calcium, barium, andammonium salts, neutral or not neutral, and of varying solubilityproperties dependent on the molecular weight.

While the conditioned pulp is in the conditioner, and before it issubjected to aeration, I add my hydrocarbon oil, which may be any inerthigh boiling oil, such as, for example, lube oil, diesel oil, mineraloil, fuel oil, kerosene or mixtures thereof. The quantity of oil I addwill depend on the nature of the pulpspecifically, the nature of thefoam produced when such pulp is agitated. The optimum quantity isreadily determined by simple experiment. Recommended proportions of oillie within the range of about 3 to 12 (preferably about 6 to pounds perton of clay feed (dry clay basis). When the postconditioning oil is usedin amount less than about 6 pounds per ton of clay feed, the treatmentloses much of its effectiveness. When used in excess of about 10 poundsper ton, the oil treatment impairs the collection. I have obtainedexceptional results with oil of about 15 to API gravity, although otheroils, such as oils heving an API gravity as low as about 12 and as highas about may be used. it will be readily apparent that the quantity ofoil I employ is considerably in excess of the amount of oil used as anauxiliary col lector reagent in various prior art flotation processes.The oil must be lightly agitated with the conditioned pulp before air isintroduced thereto and the oil conditioning may be carried out in aconditioning machine or in the flotation cell with the air off.

Referring to the flowsheet shown in the drawing, it is evident that theprocess illustrated involves four distinct froth flotation steps in acontinuous process. The first step involves continuously feeding a pulpof raw clay feed which has been conditioned with a negative-ioncollector reagent and oiled carrier particles, and then with hydrocarbonoil, as described above, to a 5 cell flotation machine, therebycontinuously obtaining from each cell a froth which is withdrawn andcombined in a launder to form a first froth product and a beneficiatedclay machine discharge product from the fifth cell.

The first froth product is continuously fed into a second flotationmachine, this one containing 4 cells; the froth product from the firstcell of this machine is continuously withdrawn separately from the frothproducts of the second, third and fourth cells which are continuouslywithdrawn in a common launder. In like manner, the froth product in thefirst cell of the third machine (which operates on the froth product ofthe second, third and fourth cells of the second machine) is discardedseparately from the froth products of the second, third and fourth cellsof the third machine. The latter froth products, as in the secondmachine, are combined in a common launder and are further refloated in afourth machine, thereby producing a froth product, all of which is sentto waste and a machine discharge product which is combined with themachine discharge product of the first, second and third machines in theusual manner.

While a four machine flotation operation is illustrated, with the twointermediate machines operated in a manner such that the froth productof the first cell is separated from the froth of subsequent cells in themachines, it will be understood that the process may be operated with 5flotation machines or more.

Although the accompanying flowsheet and the description of my inventionrefer to the fact that various froth products go to waste, it will beclearly understood that such terminology is used merely to simplify theexplanation of my invention and focus upon its essential features. Thus,the froth which goes to Waste may be further treated for separation ofthe carrier from colored impurities.

The continuous process, described immediately above, may be carried outin existing flotation equipment which is modified only to the extentthat the launder line to the first cell of each of the intermediatelines is blocked off and discharge lines for handling the froth productsfrom each of the first cells are provided.

The following examples illustrate the benefits of postconditioni-ng areagentized dispersed admixed aqueous pulp of kaoline clay and calcitecarrier with hydrocarbon oil, in accordance with this invention.

The clay used in all of the tests was a crude sedimentary Georgiakaolin. The clay was used in the form of a soduim silicate dispersedaqueous slip which was prepared -by stirring the crude kaolin clay at26% to 28% solids with deionized water until practically all of the claylumps were disintegrated. The slurry was screened to remove all plus 325mesh grit. The degritted clay had a particle size distribution such that98% by weight was minus 15 microns and was minus 1.5 micron (allparticle sizes referring to equivalent spherical diameters, asdetermined by the Casagrande water sedimentation method). The slurry wasdispersed with 0.4% (based on the dry clay weight), of sodium silicatein a Fagergren flotation machine (air 01f).

EXAMPLE I his example demonstrates the improved yield of beneficiatedclay that is realized in a batch flotation test by postconditioning thereagentized admixed clay-carrier pulp with hydrocarbon oil, inaccordance with this invention.

Control Carrier Flotation Test While the Fagergren flotation machine wasrunning with the air off, No. 1 white calcite was added to the sodiumsilicate dispersed kaolin clay pulp in the machine in the amount of 30%(based on the dry clay weight). The calcite was 98% by weight finer than40 microns, 35% minus 10 microns, and 10% minus 3 microns. After 30seconds of agitation, the following reagents were added to the admixedpulp in the order indicated: Ammonium sulfate, 6 pounds; ammoniumhydroxide, 4.0 pounds; and an aqueous emulsion containing 4.5 poundstall oil and 4.5 pounds of a commercial oil-soluble neutral calciumsulfonate complex, analyzing about 41% calcium sulfonate complex and thebalance substantially all mineral oil. All reagents are reported on thebasis of pounds per ton of dry clay in the pulp. The conditioned slurrycontaining about 750 grams of clay (dry basis) was transferred to a 1000gram Minerals Separation Airflow flotation machine, diluted to about 25%solids with soft water and subjected to froth flotation removing a frothproduct for 10 minutes. The first froth product was refioated a threeadditional times without addition of reagents and all machine dischargeproducts combined.

Flotation Tests Using Hydrocarbon Oil Conditioning Reagent The procedurefollowed in carrying out the control test was repeated in every detailthrough the step of adding the ammonium sulfate, ammonium hydroxide andemulsified tall oil collector reagent and conditioning for minutes. fiedin the accompanying table, were added to the pulp and the wholeconditioned for 12 minutes, making for a total conditioning time of 17minutes. As in the control flotation test, the conditioned pulpcontaining 750 grams of dry clay solids was transferred to a 100 gramMinerals Separation Airflow machine, diluted to about 25% solids withsoft water and subjected to flotation removing a froth product forminutes. The first froth product was refioated three additional timesand all of the machine discharge products were combined.

The clay brightness values referred to in the table were obtained byTAPPT Standard Method T-646 ltd-54, as described on pages 159A and 160Aof the October 1954 issue of TAPPI (a monthly publication of theTechnical Association of Pulp and Paper Industry). The method measuresthe light reflectance of a clay sample and thus gives a quantitativeindication of its brightness or whiteness.

The data reported in the table bring out the fact that bypostconditioning the admixed reagentized kaolin claycalcite pulp withvarious hydrocarbon oils, an improvement in recovery of beneficiatedclay was realized in all instances. With some of the oils, anexceptional improvement in clay recovery was realized. Also shown isthat in some instances a slight improvement in clay grade was obtainedsimultaneously with the improvement in clay recovery.

EXAMPLE II The following example illustrates the benefit, in acontinuous flotation operation, of refioating the froth product of thehydrocarbon oil conditioned admixed pulp and discarding the initialfroth of the cleaner flotation operation and further refloati'ng theremainder of the froth from the cleaner flotation, in accordance with aform of this invention.

The starting clay was the discolored unf-ractionated sedimentary Georgiakaolin used in the previous example. As in that example, the clay was inthe form of a sodium silicate dispersed clay slip containing 10% claysolids and 0.4% sodium silicate (based on the dry clay weight).

A control test was carried out using the four machines illustrated inthe flowsheet but with the first cell of the second and third machinesopen to the launder line in the Thereafter, various hydrocarbon oils,identi-' ver machine, with 5, 4, 4 and 3 cells in series, asillustrated. In a continuous pilot plant operation employing about 1064pounds per hour of the crude kaolin clay (dry basis), about 320 poundsper hour of natural calcite (No. 1 White) was added to the silicatedispersed clay slip. The particle size of the calcite was 98% by weightminus 40 microns, 36% minus 10 microns, and 10% minus 3 microns. Thedispersed admixed pulp of crude clay and calcite was conditioned in theorder given, with about 6 pounds of ammonium sulfate, an emulsifiedmixture of 4.5 pounds crude tall oil fatty acid and 4.5 pounds of aneutral oil-soluble petroleum sulfo-nate, analyzing 41% calciumsulfonate complex and the balance substantially all mineral oil.Conditioning time was 5 minutes. Eight pound of Eureka M lube oil wasadded to the pulp and conditioned for 12 minutes. Sufiicient ammoniumwas added to maintain a pH of about 8.5 in the conditioned pulp. Allreagents are reported on the basis of pounds per ton of the dry clayfeed. The percent solids in the conditioner was about 18%.

The conditioned pulp was continuously fed to the 5 cell No. 1 flotationmachine, with dilution water added to the second, third and fourthcells. A machine discharge product was taken from the fifth cell whichwas a slip of high brightness kaolin clay amounting to about 58%, weightbasis, of the original kaolin clay. The froth product from thisoperation was continuously refioated in an additional machine, inaccordance with conventional flotation practice, with the froth productfrom each of the four cells in the second machine being combined andrefioated in a third machine. This procedure was repeated in the thirdmachine, i.e., the entire froth product from the second machine wasrefloated and the froth from each of the cells in the third machine werecombined. The combined froth product from the third machine wascontinuously fed to a 3 cell fourth machine, thus producing a finalfroth product which was sent to waste and a machine discharge productwhich was combined with the machine discharges from the first, secondand third machines to yield about 84% weight recovery of kaolin clay ofimproved brightness containing a very small percentage of TiO and othercoloring impurities.

A second test was carried out to illustrate the advantage of operatingthe general process described in the first test, in accordance with themethod of this invention. The first test procedure was duplicated inevery respect, except that provision was made to pass directly to wastethe froths from the first cells of machines N0. 2 and No. 3, as shown inthe flowsheet. The brightness of the combined machine discharges of thistest was substantially the same as that of the first test product.However, about a 10% improvement in weight recovery of beneficiated claywas realized, thereby illustrating the value of discarding the initialfroth product from the cleaner flotation conventional manner. Eachmachine wasa No. 8 Denoperations.

THE RESULT OF POSTCONDITIONING REAGENTIZED ADMIXED PULP OF DISCOLOREDKAOLIN CLAY 1 AND GALCIIE CARRIER WITH VARIOUS HYDROCARBON OILS OilBeneficiated Clay Product Lbs. Oil/ Unbleached Increase in TypeHydrocarbon O11 Ton Clay API Wt. Brightness, Brightness,

Feed (Dry Gravity Percent Percent Percent Clay Basis) None 90. 5 83.7 4.8 95% Bunker C, 5% Diesel Oil 8 91. 9 83.8 4. 9 90% Bunker C, 10% DieselOil. 8 94.1 83. 9 5.0 85% Bunker C, 15% Diesel Oil- 8 3 83. 9 5.0 80%Bunker C, 20% Diesel Oil 8 96. 4 84. 0 5. 1 75% Bunker C, 25% DieselOiL.-- 8 95. 7 83. 9 5.0 Bunker O, 30% Diesel Oil. 8 95. 7 83. 9 5.0Eureka h! Lube Oil, 25% M 8 92. 7 83. 9 5. 0 Eureka lvi Lube Oil" 8 91.9 83. 7 4. 8 Ebony Oil 8 93. 5 83. 5 4. 6 Conventional ParafiinicNeutral Oil 8 98. 1 83. 7 4. 8 Solvent Neutral Oil 8 97. 5 83. 9 5.0

1 Unbleached brightness of Starting Clay was 78.9%.

I claim:

1. In the method for improving the brightness of kaolin clay havingcolor body impurities mechanically associated therewith comprisingforming a dispersed aqueous pulp of said clay, without any grindingaction conditioning said pulp for froth flotation with a negative-ioncollector reagent capable of selectively oiling said color bodyimpurities and collector-coated particles of an auxiliary mineral, saidparticles being further characterized by being floatable in said pulp,and subjecting the thus conditioned pulp to froth flotation at a pHwithin the range of 8 to 10, thereby producing a froth product which isa concentrate of said color body impurities in intimate association withsaid auxiliary mineral particles and a machine discharge product whichis a concentrate of clay of increased brightness, the improvement whichcomprises further conditioning said aqueous pulp of clay with ahydrocarbon oil after it has been conditioned with said negative-ioncollector reagent and said collector-coated auxiliary mineral particlesand before said pulp has been subjected to an initial froth flotation.

2. The method of claim 1 wherein said oil is employed in amount of 6 to10 pounds per ton of dry clay feed.

3. The method of claim 1 wherein said oil has an API gravity of about 12to 25.

4. The method of claim 1 wherein said oil has an API gravity of about 15to 20.

5. The method of claim 1 wherein said pulp is conditioned with said oilfor about 12 minutes.

6. The method of claim 1 wherein all of the first froth product isrefloated, discarding the initial froth and refloating the balance ofthe froth.

7. The method of claim 1 wherein the froth product is continuouslyrefloated in separate machines, each containing a plurality of cellsarranged in series, and the froth product from the first cells of eachmachine is separated from the froth product of the remaining cells andthe froth product from said remaining cells further subjected to frothflotation.

8. In a method for beneficiating a slimed multicomponent mineral masswhich comprises forming a dispersed aqueous pulp of said mass,conditioning said aqueous pulp for froth flotation with a collectorreagent selective to a component of said mass, leaving a residualcomponent water-wettable, and with collector-coated particles of anauxiliary mineral, said particles being further characterized by beingfloatable in said pulp, and subjecting the thus conditioned aqueous pulpto froth flotation thereby producing a froth product which is aconcentrate of said collector-coated component of said mass in intimateassociation with said auxiliary mineral particles and a machinedischarge product which is a concentrate of said water-wettablecomponent of said mass, the: improvement which comprises conditioningsaid aqueous pulp with a hydrocarbon oil after it has been conditionedwith said collector reagent and said collector-coated particles of anauxiliary mineral and before it has been subjected to an initial frothflotation, and carrying out the flotation of the resulting pulp in amanner such that all of the first froth product is refloated, theinitial refloated froth is separated and the balance of the refloatedfroth is refloated to obtain additional froth products and machinedischarge products.

9. The method of claim 8 wherein the machine discharge product containsa valuable mineral and the machine discharge products of all of thefiotations are combined, whereby an increase in product. recovery isobtained.

10. The method of claim 8 wherein said first froth product iscontinuously refloated in separate machines, each machine containing aplurality of cells arranged in series, and the froth product from thefirst cells is separated from the froth product of the remaining cellsand the froth product from said remaining cells is further subjected tofroth flotation.

References Cited in the file of this patent UNITED STATES PATENTS2,165,268 Vogel-Jorgensen July 11, 1939 2,259,420 Hills Oct. 14, 19412,373,688 Keck Apr. 17, 1945 2,569,680 Leek Oct. 2, 1951 2,669,355Archibald Feb. 16, 1954 2,695,101 Booth Nov. 23, 1954 2,849,113 BourneAug. 26, 1958 2,894,628 Duke July 14, 1959 2,984,348 Adams et a1 May 16,1961 2,990,958 Greene et al. July 4, 1961 FOREIGN PATENTS 610,817 GreatBritain Oct. 21, 1948

1. IN THE METHOD FOR IMPROVING THE BRIGHTNESS OF KAOLIN CLAY HAVINGCOLOR BODY IMPURITIES MECHANICALLY ASSOCIATED THEREWITH COMPRISINGFORMING A DISPERSED AQUEOUS PULP OF SAID CLAY, WITHOUT ANY GRINDINGACTION CONDITIONING SAID PULP FOR FROTH FLOTATION WITH A NEGATIVE-IONCOLLECTOR REAGENT CAPABLE OF SELECTIVELY OILING SAID COLOR BODYIMPURITIES AND COLLECTOR-COATED PARTICLES OF AN AUXILIARY MINERAL, SAIDPARTICLES BEING FURTHER CHARACTERIZED BY BEING FLOATABLE IN SAID PULP,AND SUBJECTING THE THUS CONDITIONED PULP TO FROTH FLOTATION AT A PHWITHIN THE RANGE OF 8 TO 10, THEREBY PRODUCING A FROTHE PRODUCT WHICH ISA CONCENTRATE OF SAID COLOR BODY IMPURITIES IN INTIMATE ASSOCIATION WITHSAID AUXILIARY MINERAL PARTICLES AND A MACHINE DISCHARGE PRODUCT WHICHIS A CONCENTRATE OF CLAY OF INCREASED BRIGHTNESS, THE IMPROVEMENT WHICHCOMPRISES FURTHER CONDITIONING SAID AQUEOUS PULP OF CLAY WITH AHYDROCARBON OIL AFTER IT HAS BEEN CONDITIONED WITH SAID NEGATIVE-IONCOLLECTOR REAGENT AND SAID COLLECTOR-COATED AUXILIARY MINERAL PARTICLESAND BEFORE SAID PULP HAS BEEN SUBJECTED TO AN INITIAL FROTH FLOTATION.